Related to the question about who can see Force Ghosts, I'm curious if they're limited in their reach? Are they able to go anywhere in the Galaxy, or are they limited to people and places with high Force concentrations? While they (might, based on the linked question) only be limited to being viewed by Force Sensitives, it seems like the various force ghosts we've seen would make excellent spies and rabble-rousers for the Rebels / Resistance if they were to be used that way. Even if they can only commune with Force Sensitives, they could be quite useful in an asymmetric capacity.
So, core question is in the Title: Do we know from (any level of canon) whether they are limited in where they can go?